micro Mondays: Zooming in with SEM

Last week we introduced the technique of Scanning Electron Microscopy (SEM) and posted an electron micrograph (SEM image) of a hexagonal alumina/hematite crystal formed in a “flashing” region on the surface of a ceramic vessel from an atmospheric firing. We noted that SEM is capable of capturing images with resolution much finer than the limit of optical microscopy, which is roughly a few hundred nanometers. In the gallery of images below, we show a sequence of images that zoom in on the bottom edge of the hexagon to reveal very fine scale details. I’m not sure what the structures correspond to in terms of material composition, but I think it’s impressive to see the kind of magnification obtainable through SEM! Having this capability in general makes it possible for us to study nanocrystals on ceramic surfaces that are much too small to be resolved sharply with an optical microscope, yet when present in large numbers contribute significantly to the appearance of the ceramic surface to our bare eyes.

It’s interesting to note the triangular protrusions from the bottom of the hexagon — these may show something about how either the alumina crystal grows or how hematite starts to form along its edges. When it comes to crystallography hexagons and triangles are closely related.

K-12 STEAM Connections: What is meant by three-fold or six-fold symmetry? How would you make a hexagon out of triangles? What types of microscopy, if any, can currently be used to study material surfaces with atomic resolution?

Acknowledgments: Part of this work was performed at the Stanford Nano Shared Facilities (SNSF) of Stanford University.